Natural environmental cues and circadian rhythms of behaviour--a perspective

Natural environmental cycles are often extremely difficult to reproduce under laboratory conditions. Laboratory light-dark cycles differ from natural light-dark cycles in terms of intensity and spectral distribution, whilst simulated temperature cycles may differ from natural temperature cycles in waveform. The expression of a free-running rhythm depends upon the 'level' of constant conditions provided. Environmental cues affect the period, phasing, amplitude and activity-rest ratios of circadian rhythms and, if inappropriate, may result in aberrant behaviour patterns which are unlike those observed in nature.